In this case, the term a continuous flow machine means, in particular, a steam turbine. Steam turbines are subdivided into so-called high-pressure, medium-pressure or low-pressure turbine elements. At the moment, there is no standard subdivision of steam turbines into the abovementioned turbine elements. In general, a high-pressure turbine element has steam applied to it at a temperature of up to 620° C. and at a pressure of up to 350 bar. The steam flowing out of this high-pressure turbine element is heated in an intermediate superheater back to a temperature of up to 620° C. and then flows into the medium-pressure turbine element, with the steam then flowing out of the medium-pressure turbine element into the low-pressure turbine element. In general, steam turbines are designed with an inner housing based on the so-called two-shell or three-shell design.
By way of example, in a medium-pressure turbine element, the medium-pressure outlet steam flows around the inner housing. Depending on the circuit parameters, this medium-pressure outlet steam may be at comparatively low temperatures, thus leading to a comparatively high temperature difference between the inner housing inner wall and the inner housing outer wall. The so-called hot intermediate-superheated steam is applied to the inner housing inner wall, with the medium-pressure outlet steam flowing around the inner housing outer wall, as described above. Since the temperatures of the medium-pressure outlet steam and of the hot intermediate-superheated steam are comparatively different, this leads to different thermal loads on the inner housing. The high temperature differences lead to unacceptably high loads for example on the screws joining the elements and on the inner housing, which can lead to increased elastic and/or plastic housing deformation.
As a precaution against this housing deformation, it is now normal practice to encase the inner housing with steel sheets, in order to prevent medium-pressure outlet steam from flowing directly onto the inner housing outer surface. The casing is frequently referred to as a heat protection jacket or as a thermal shield, and is arranged around the entire inner housing. In order to maintain comparatively uniform environmental conditions, temperature distributions and uniform or low flow rates of the medium-pressure outlet steam on the inner housing surface, the heat protection jacket is designed such that gaps are created between the heat protection jacket and the inner housing. Furthermore, additional openings are arranged in the heat protection jacket, in order to allow the medium-pressure outlet steam to flow through the heat protection jacket.
This has the disadvantage that the actual conditions within the heat protection jacket are virtually impossible to change. This means that the actual conditions cannot be matched to the requirement for the inner housing. In this case, it would be desirable for it to be possible to adjust the temperature within the heat protection jacket. This means that it would be advantageous to deliberately increase or reduce the temperature within the jacket.